get_statistics: Measure statistics of NSS
In QinglongYan/ANSSI: Automated near-stationary state identifier

This function is applied to measure quantity and quality of identified near-stationary states in the congested regime.

1	get_statistics(datasets, critical, tolerance)

`datasets`	The datasets of identified near-stationary states in the list format.
`critical`	Pre-determined critical density by prior knowledge, e.g. 0.18
`tolerance`	Minimum acceptable sample size; R-squared would be regarded zero if the sample size is smaller than the tolerance.